The invention relates to a method for controlling a drive system and/or a wheel braking system of a vehicle.
For motor vehicles having driver assistance systems by which, in particular, a predetermined speed or a predetermined distance from the vehicle traveling ahead is to be held constant, methods are known for controlling a drive system and/or a wheel braking system to achieve the driver assistance objectives. In this regard, however, problems continually arise, in particular for downhill travel. Either the wheel braking systems become very hot, or actions of the drive system, such as downshifting of the automatic transmission or changing the type of overrun mode (fired/unfired), result in sacrifices in comfort.
The invention provides an improved method for controlling a drive system and/or a wheel braking system, in particular for downhill travel, with regard to comfort, while at the same time taking into account a reduction in the load on the wheel braking system.
According to the invention, a method for controlling a drive system and/or a wheel braking system of a vehicle, in which a total brake power (Ptotal—wheel—setpoint) to be exerted on the wheels of a motor vehicle is composed of a drive braking power (Pdrive—wheel—setpoint) and/or a wheel braking power (Pbrake—wheel—setpoint), is characterized in that the instantaneously set drive braking power (Pdrive—wheel—actual) or the instantaneously specified drive braking power (Pdrive—wheel—setpoint) is frozen when, starting from a steady state operating mode, the gradient of the required total braking power (Ptotal—wheel—setpoint) exceeds a predetermined threshold (S). Advantageous refinements of the invention are described and claimed herein.
For downhill travel, the invention is used in particular when, starting from a steady state operating mode, i.e., in particular for travel at an approximately constant speed, an intention to decelerate occurs, as the result of which the required total braking power instantaneously changes in a relatively intense manner. Such an intention to decelerate may be provided either by the driver via manual adjustment of the specified vehicle speed, or by the system itself when the distance from the vehicle traveling ahead drops below a predetermined value.
The total braking power may be specified, for example, by the driver's intent, determined by an interpretation of a brake and/or accelerator pedal, or by a driver assistance system (cruise control, ACC, etc.). The invention is particularly advantageous when used in motor vehicles having driver assistance systems based on the principle of maintaining a constant predetermined speed.
The wheel braking power is the proportion of the total braking power exerted on the wheels, which is performed by the wheel braking system.
The drive braking power is, preferably, the proportion of the total braking power exerted on the wheels, which is performed by the total drive system including at least one engine and a transmission, whereby both the engine and the transmission may be electronically controllable.
The present invention prevents uncomfortable transmission downshifting and/or abrupt changes in engine torque as the result of the transition from unfired to fired overrun mode, and vice versa.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.